Vertebrate visual cells are investigated in optical isolation with a unique dichroic microspectrophotometer (DMSP). Absorbance and linear dichroism spectra are simultaneously measured from 275 nm and up through the visible spectrum. The long-term objectives are 1, a quantitative description of color vision, 2, an understanding of the biology of spectral tuning in visual pigments and, 3, a detailed knowledge of the visual cycle, i.e., the chemical forms of the retinoids as they bleach and regenerate visual pigments. The specific aims are: 1. The redetermination of human visual pigment absorbance spectra; 2. The study of the chemical properties and three-dimensional disposition (chromophore orientation) of visual pigments in rods and cones, including the ultraviolet (UV) absorbing types; 3. The determination of the ellipsosomes' biochemical role in the killifish retina as they probably subserve the energy generating needs of photoreceptors; 4. The study of visual pigment regeneration inlarval tiger salamander cones and rods; 5. The study of retinoid transformations in gecko and carp photoreceptors; 6. The continued development of the DMSP. The design of the experiments is based on the observation that most vertebrate photoreceptors, in freshly excised retinal tissue, can be maintained in physiological solutions and examined in the light microscope before major cellular deteriorations set in. Histochemical techniques ar combined with light microscopic observations and microspectrophotometric measurements of single subcellular compartments. The overall objective is a quantitative understanding of the cellular basis of vision. This work may be relevant to retinal degenerative diseases and to human color vision, abnormal (color blindness), as well as normal.